$ B = \left[\begin{array}{rrr}1 & 1 & 2 \\ 2 & 1 & 1 \\ 1 & 0 & 1\end{array}\right]$ What is $ B^{-1}$ ?
Answer: $ = \left[\begin{array}{rrr}-\frac{1}{2} & \frac{1}{2} & \frac{1}{2} \\ \frac{1}{2} & \frac{1}{2} & -\frac{3}{2} \\ \frac{1}{2} & -\frac{1}{2} & \frac{1}{2}\end{array}\right]$